The present invention relates to systems for joining together the ends of adjacent duct sections, such as heating and air-conditioning ducts or the like. Such systems typically include generally L-section connectors respectively fastened to the end edges of each of the duct walls, each connector having a leg portion which projects outwardly from the duct wall perpendicular thereto and defines an elongated channel. The channels of connectors on intersecting duct walls respectively receive therein the legs of a corner member. The corner members on the adjacent duct sections are then fastened together. A suitable gasket may be disposed between the duct sections.
Prior systems have been relatively expensive to manufacture and difficult to install. Many such systems have required that the connectors be secured to the duct walls by numerous fasteners or spot welds, either of which entails costly and time consuming labor. Some systems have utilized tabs on the duct walls which engage lips on the connectors to inhibit separation of the duct walls from the connectors. The lip is on a flexible portion of the connector to facilitate engagement, but this same flexibility could also permit disengagement when the duct system was subjected to certain stresses. Furthermore, the duct wall is pierced to form the tabs, resulting in air leakage at the tabs.
Many systems provide inadequate sealing at the joint between the duct sections, permitting escape of air from the duct. In some prior systems the connector carries a body of mastic sealant material into which the associated duct edge is embedded. These systems have had connector constructions which make it difficult to install the sealant and which do not facilitate insertion of the duct edge thereinto. Improper seating of the duct edge in the sealant permits leakage. Also, where a gasket is used it does not adhere well to the corner members of prior systems, resulting in leakage at the corners of the duct joints, particularly in pressurized systems. With the ever-increasing emphasis on energy conservation, leakage is an increasingly significant problem. Duct assembly systems and, particularly, the corner members thereof, must have sufficient strength and rigidity to meet construction industry standards and to prevent deformation during handling, assembly or use of the duct system. Yet, at the same time, such assembly systems should be lightweight to minimize the cost of construction and to minimize the loads placed on the associated building. The corner members of prior systems have typically been constructed of expensive, heavy-gauge material or have lacked the strength required by industry standards.